server:
[tru@jessejames /work]$ uname -a
Linux jessejames.bis.pasteur.fr 2.6.18-8.1.8.el5 #1 SMP Tue Jul 10 06:39:17 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux
[tru@jessejames /work]$ cat /etc/exports 
/work/ro calamityjane.bis.pasteur.fr(ro,async)
/work/rw calamityjane.bis.pasteur.fr(rw,async)
[tru@jessejames ~]$ showmount -e
Export list for jessejames.bis.pasteur.fr:
/work/rw calamityjane.bis.pasteur.fr
/work/ro calamityjane.bis.pasteur.fr

client:
[tru@calamityjane ~]$ uname -a
Linux calamityjane.bis.pasteur.fr 2.6.18-8.1.8.el5 #1 SMP Tue Jul 10 06:50:22 EDT 2007 i686 i686 i386 GNU/Linux
[tru@calamityjane ~]$ tail -4 /etc/fstab
# nfs testing c5
jessejames.bis.pasteur.fr:/work/ro /mnt/ro nfs defaults,ro,noauto  0 0
jessejames.bis.pasteur.fr:/work/rw /mnt/rw nfs defaults,rw,noauto  0 0 <-- typo fixed
[tru@calamityjane ~]$ mount|grep mnt
jessejames.bis.pasteur.fr:/work/ro on /mnt/ro type nfs (ro,addr=157.99.90.171)
jessejames.bis.pasteur.fr:/work/rw on /mnt/rw type nfs (rw,addr=157.99.90.171)

[tru@calamityjane ~]$ mkdir /mnt/ro/d
mkdir: cannot create directory `/mnt/ro/d': Read-only file system
[tru@calamityjane ~]$ mkdir /mnt/rw/d
mkdir: cannot create directory `/mnt/rw/d': Read-only file system